This invention relates to a pressure modulator arrangement for a boosting of brake force and for antilock control for a vehicle with a power-assisted hydraulic multiple-circuit brake system having closed statically operated brake circuits.
In the case of a known pressure modulator arrangement of this type, one pressure modulator is provided for each of the total of four wheel brakes of the vehicle. The output pressure of one or the other output pressure space of a tandem master cylinder, that is provided as a brake-pressure control device and can be pedal-operated via a hydraulic or a pneumatic brake booster of the conventional type, can be coupled into the connected wheel brake via the pressure modulator. Each of the pressure modulators has a modulator piston that can be slid in a pressure-sealed manner in a housing. The modulator pistons each have two flanges that are connected with one another by means of a piston rod that is guided through a central bore of a partition of the modulator housing so that it can be slid in a pressure-sealed way. The output pressure space of the respective modulator to which the assigned wheel brake is connected is delimited by one flange and this partition.
The input pressure space of the modulator that is connected with one of the control output pressure spaces of the tandem master cylinder is delimited by the other piston and the partition. By admission of pressure to the input pressure space, the modulator piston is shifted in the sense of a reduction of the output pressure space, resulting in the building-up of brake pressure in the connected wheel brake. Two each of these modulators are housed in a joint housing part in such a way that the flanges of their modulator pistons, that in each case delimit the input pressure space on one side, jointly delimit a counterpressure space in the axial direction. By the admission of pressure to counterpressure space during a control phase of the antilock system, the modulator pistons shift in the sense of an enlargement of the volumes of the output pressure reduction in the connected wheel brake. Into the two counter pressure spaces of this pressure modulating device, the high output pressure of a pressure accumulator can be coupled simultaneously or alternately, under the control of electro magnetic valves. the pressure accumulator is maintained constantly in a charged state by means of an accumulator charge pump. The control-effective triggering of the pressure-reduction control valves takes place by means of output signals of an electronic control unit of the antilock system.
A main disadvantage in the case of the known pressure modulator arrangement is that the modulator pistons, in a pressure-reduction control phase, must be shifted against a high pressure in the respective modulator input pressure space generated with the participation of the brake force booster. Thus accumulator charge pump must be designed for a very high nominal capacity, the typical value of which is 200 w. However, a hydraulic pump that is designed for such a high nominal capacity and output pressures of around 200 bar requires not only a relatively large overall space but is also very expensive and therefore significantly contributes to the costs of an antilock system comprising the pressure modulator arrangement. Because of the required high nominal capacity of the accumulator charge pump, the electrical wiring of the vehicle must also be designed for a higher output power.
It is therefore the objective of the invention to provide a pressure modulator arrangement of the initially mentioned type that, while it also has a simple construction and good operational reliability, on the whole can operate with a charge pump that is designed for a clearly lower nominal capacity, for a pressure accumulator that is utilized as an auxiliary pressure source.
This and other objectives are achieved by the pressure modulators having a first driving pressure space into which the output pressure of the brake-pressure control device is coupled and a second driving pressure space into which the output pressure of a proportional control valve, which is proportional to the pedal force and causes the brake-force boosting, is coupled. A counterpressure space is also provided. In addition, a control valve arrangement is provided which, upon actuating by the antilock control, the second driving pressure space is blocked with respect to the auxiliary pressure source or is relieved of pressure. The admission of pressure to the counter pressure space shifts the modulator piston only against the force resulting from the admission of pressure to the first control pressure space. Thus, against a significantly smaller actuating force than in the case of a normal braking. The accumulator charge pump can thus be designed for a significantly lower nominal capacity, compared with the known pressure modulator arrangement. In practice it is about half the nominal capacity. This results in a considerable lowering of the manufacturing costs. In addition, in the case of the development of the pressure modulators provided according to the invention, the pressure modulator is also utilized as an auxiliary force source for the brake-force boosting which results in a further constructional simplification.
Appropriate selection of the areas of the elements of the pressure modulators has the advantage that, when the auxiliary pressure source is inoperative, i.e., when there is no brake-force boosting, braking can still take place with a good braking deceleration - with a prolonged pedal travel.
By using two the control valves, the appropriate brake pressure control can be realized alternatively or in combination.
A proportional control valve can be integrated in a simple way into a hydraulic unit comprising several pressure modulators. In which case, the hydraulic unit may be arranged away from the brake pressure control device and can be triggered hydraulically. Also, by providing two input pressure spaces in the proportional control valve increased protection is achieved with respect to a partial breakdown of the control circuits of the brake-pressure control device.
By means of a single additional control valve a propulsion control function can also be achieved in a simple way by the present modulator.
Other details and characteristics of the invention are found in the following description of special embodiments by means of the drawing.